1. Field of the Invention
The present invention relates generally to air conditioners, and, more particularly, to automotive air conditioners, especially useful for electric vehicles.
2. Description of Related Art
The advent of an international agreement limiting production of certain refrigerants because of their detrimental effect on the atmosphere, particularly the depletion of the ozone stratospheric layer, has caused a sudden and intense concern in the refrigeration and air conditioning industry. As is well-known, the Montreal Protocol has been signed by 24 nations, including the United States, and efforts are going forward to put its provisions into effect. The signatory nations in the Montreal Protocol have agreed that chlorofluorocarbons (CFCs) will be strictly controlled and that all production will cease in 1995. The Environmental Protection Agency (EPA) has released a massive collection of rules and regulations that will be used to enforce cuts in the production and use of these refrigerants. During the second half of 1992, the EPA can begin enforcing these laws outlined in the 1990 U.S. Clean Air Act. Earlier this year, the U.S. administration implemented an accelerated phase-out schedule. According to the EPA rules, the sale of CFCs to the public becomes illegal. It is also illegal for anybody, including service persons, to vent CFCs in the air. Moreover, the law requires the collection and recycling of all the refrigerants in automotive applications. Anyone servicing an air conditioner must be EPA-certified and must use approved recovery and recycling equipment.
The refrigerants in question are the chlorofluorocarbons (CFCs) 11, 12, 113, 114, and 115. Of these, the banning of CFC-12 is of the utmost concern, as it is used in refrigerators, freezers, automobile air-conditioners, refrigerated vending machines, food display cases, and a variety of small home and business appliances. Moreover, of the aforementioned uses of CFC-12, the automobile air-conditioner one is the most critical use, as it comprises the largest inventory of the refrigerant as well as it offers the highest likelihood of escape to the environment.
In the past few years the hydrofluorocarbon (HFC) 134a has been promoted as a substitute for CFC-12 in automobile air-conditioners. However, HFC-134a is not a drop-in replacement for CFC-12. The thermophysical properties of HFC-134a are such that it requires a bigger compressor, heavier fluid lines, and is not as efficient as CFC-12(fuel requirements are calculated to be 4% higher using HFC-134a compared to that of CFC-12). In addition, performance comparisons in vehicles between CFC-12 and HFC-134a show that the passenger compartment temperature is 1.degree. to 2.degree. F. (0.56.degree. to 1.1.degree. C.) higher at normal vehicle speed, and 4.degree. to 6.degree. F. (2.2.degree. to 3.3.degree. C.) higher at idle when HFC-134a is used.
It is therefore prudent to investigate other refrigeration alternatives, particularly with regard to automotive air-conditioning uses.
However, while there is a concern regarding the banning of CFCs, it will also be recognized that there are numerous applications where a potentially more energy efficient system may be desirable or necessary than the traditional vapor compression cycle, whether it makes use of CFC-12 or HFC-134a. Such is the case, for example, in an electric vehicle where a traditional air-conditioner draws significant amounts of power that reduce critically the in-between charging range of the vehicle. Electric vehicles, of course, are also becoming highly desirable because of reduced emissions of carbon dioxide and several air pollutants.
Thus, increased efficiency becomes a very important driving force regarding the development of alternative automotive air-conditioning systems.